package com.egghiro.framework.j2se.util.hash;

/**
 * 
 * Copy from Baidu Baike
 * http://baike.baidu.com/view/273836.htm?fromtitle=Hash%E7%AE%97%E6%B3%95&fromid=5737278&type=syn
 * 
 */
public class GeneralHashFunction {
    
    public static long RSHash(String str) {
        int b = 378551;
        int a = 63689;
        long hash = 0;
        for (int i = 0; i < str.length(); i++) {
            hash = hash * a + str.charAt(i);
            a = a * b;
        }
        return hash;
    }

    public static long JSHash(String str) {
        long hash = 1315423911;
        for (int i = 0; i < str.length(); i++) {
            hash ^= ((hash << 5) + str.charAt(i) + (hash >> 2));
        }
        return hash;
    }

    public static long PJWHash(String str) {
        long BitsInUnsignedInt = (long) (4 * 8);
        long ThreeQuarters = (long) ((BitsInUnsignedInt * 3) / 4);
        long OneEighth = (long) (BitsInUnsignedInt / 8);
        long HighBits = (long) (0xFFFFFFFF) << (BitsInUnsignedInt - OneEighth);
        long hash = 0;
        long test = 0;
        for (int i = 0; i < str.length(); i++) {
            hash = (hash << OneEighth) + str.charAt(i);
            if ((test = hash & HighBits) != 0) {
                hash = ((hash ^ (test >> ThreeQuarters)) & (~HighBits));
            }
        }
        return hash;
    }

    public static long ELFHash(String str) {
        long hash = 0;
        long x = 0;
        for (int i = 0; i < str.length(); i++) {
            hash = (hash << 4) + str.charAt(i);
            if ((x = hash & 0xF0000000L) != 0) {
                hash ^= (x >> 24);
            }
            hash &= ~x;
        }
        return hash;
    }

    public static long BKDRHash(String str) {
        long seed = 131; // 31 131 1313 13131 131313 etc..
        long hash = 0;
        for (int i = 0; i < str.length(); i++) {
            hash = (hash * seed) + str.charAt(i);
        }
        return hash;
    }

    public static long SDBMHash(String str) {
        long hash = 0;
        for (int i = 0; i < str.length(); i++) {
            hash = str.charAt(i) + (hash << 6) + (hash << 16) - hash;
        }
        return hash;
    }

    public static long DJBHash(String str) {
        long hash = 5381;
        for (int i = 0; i < str.length(); i++) {
            hash = ((hash << 5) + hash) + str.charAt(i);
        }
        return hash;
    }

    public static long DEKHash(String str) {
        long hash = str.length();
        for (int i = 0; i < str.length(); i++) {
            hash = ((hash << 5) ^ (hash >> 27)) ^ str.charAt(i);
        }
        return hash;
    }

    public static long BPHash(String str) {
        long hash = 0;
        for (int i = 0; i < str.length(); i++) {
            hash = hash << 7 ^ str.charAt(i);
        }
        return hash;
    }

    public static long FNVHash(String str) {
        long fnv_prime = 0x811C9DC5;
        long hash = 0;
        for (int i = 0; i < str.length(); i++) {
            hash *= fnv_prime;
            hash ^= str.charAt(i);
        }
        return hash;
    }

    public static long APHash(String str) {
        long hash = 0xAAAAAAAA;
        for (int i = 0; i < str.length(); i++) {
            if ((i & 1) == 0) {
                hash ^= ((hash << 7) ^ str.charAt(i) ^ (hash >> 3));
            } else {
                hash ^= (~((hash << 11) ^ str.charAt(i) ^ (hash >> 5)));
            }
        }
        return hash;
    }
}
